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A Test of Bycatch Reduction Devices on Commercial Crab Pots in a Tidal Marsh Creek in Virginia

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A Test of Bycatch Reduction Devices on Commercial Crab Pots in a Tidal Marsh Creek in Virginia Estuaries and Coasts (2011) 34:386–390 DOI 10.1007/s12237-010-9330-1 NOTE A Test of Bycatch Reduction Devices on Commercial Crab Pots in a Tidal Marsh Creek in Virginia A. Scott Morris & Stephanie M. Wilson & Erik F. Dever & Randolph M. Chambers Received: 15 October 2009 /Revised: 5 July 2010 /Accepted: 7 July 2010 /Published online: 21 July 2010 # Coastal and Estuarine Research Federation 2010 Abstract The effectiveness of bycatch reduction devices declines in population sizes from various threats throughout (BRDs) on commercial pots designed to capture blue crabs their range have prompted many states to list terrapins as Callinectes sapidus wastestedintheYorkRiveron endangered, threatened, or a species of special concern Felgates Creek (37.2667 N, −76.5850 W) over the period (Butler et al. 2006). Because the economies of many of 4 June through 31 July 2009. For each of 10 pairs of pots, these same states are bolstered by the harvest of the blue one had BRDs affixed to all four entrance gapes and the crab Callinectes sapidus, extensive use of commercial pots other had none. Pots were baited approximately once each to catch crabs has led to bycatch mortality of terrapins week but were sampled for blue crabs and bycatch 6 of (Wood 1997; Roosenburg and Green 2000; Hoyle and 7 days each week for the duration of the study. More than Gibbons 2000; Butler and Heinrich 2007; Dorcas et al. one fourth of 1,643 total crabs were caught on the first day 2007; Grosse et al. 2009; Rook et al. 2010). New York, after baiting, and for these 7 days, no statistical difference New Jersey, Maryland, and Delaware now require a version was detected between either the number or size of legal-size of a terrapin excluder device on certain commercial pots to crabs caught in BRD versus non-BRD pots. Of 51 reduce that source of mortality, but enforcement is difficult Malaclemys terrapin and44fishcaughtasbycatch (Roosenburg 2004). throughout the study, all but three fish were captured in Terrapins typically spend most of their lives in shallow non-BRD pots. BRDs exclude bycatch and may reduce water adjacent to tidal wetlands, so during the summer, incidental mortality of crabs in pots that are not tended only a small portion of the crab fishery spatially intersects regularly. with turtle habitat (but see Roosenburg 2004). Within that shallow-water habitat, however, we recognize at least four Keywords Diamondback terrapin . Excluder . possible sources of commercial pots. First, some commer- Recreational crabbing cial hard-shell crabbers may run lines of pots along the mainstem of small tidal creeks, with daily baiting and harvesting. Second, commercial crabbers during a short Introduction period may run “peeler pots” baited with male crabs to attract female crabs ready to shed their shells prior to The diamondback terrapin Malaclemys terrapin is the only mating. Crabbers focus their effort in the relatively fully estuarine turtle in the Western Hemisphere, occurring protected habitat of small tidal creeks where peelers in coastal habitats from Massachusetts to the Gulf Coast of concentrate. Third, many recreational crabbers place one Texas (Ernst and Lovich 2009). Low numbers or measured or two commercial-type pots in shallow tidal waters near their waterfront property homes. Baiting and checking of : : : recreational pots may be infrequent. Finally, when hard- A. S. Morris S. M. Wilson E. F. Dever R. M. Chambers (*) shell crab pots placed in deeper water break free from their Biology Department and Keck Environmental Field Lab, moorings or are abandoned, they may be carried by storms College of William and Mary, Williamsburg, VA 23187, USA or tidal currents into shallow-water habitat. Though they are e-mail: [email protected] never baited, these ghost or derelict pots are potential, Estuaries and Coasts (2011) 34:386–390 387 chronic causes of bycatch mortality (Roosenburg 1991; gizzard shad (Dorosoma cepedianum) on average once each Guillory and Prejean 1998; Havens et al. 2008). week for 7 weeks during summer 2009. We chose this In most states where required, regulations to install bycatch experimental design because many recreational crabbers bait reduction devices (BRDs) on crab pots have targeted and/or check their pots infrequently; further, abandoned pots recreational crabbers, but clearly crab pots from other users are not tended at all, so the catch obtained after many days are either fished or end up in shallow-water habitat where without fresh baiting also is a potential proxy for pots that terrapins are most abundant. For the present study, we have been lost. The effects of self-baiting on crab capture by designed an experiment to test BRD function in a brackish abandoned pots, however, were not tested in this study. marsh complex. Our objective was to complete the first test of When sampling, every organism caught in a pot was BRDs in Virginia shallow subtidal waters where recreational, identified and recorded. Crabs were sexed, and point-to-point peeler, and derelict crab pots are located. By baiting pots at carapace width was measured using a sliding caliper. Legal- infrequent intervals, we were also able to assess the potential size crabs were those with carapace widths exceeding influence of some recreational pots (that are rebaited 12.5 cm. Each captured turtle was sexed and measured for infrequently) and derelict pots (that are never rebaited) on carapace width and shell depth. Finally, every newly captured crab catch and terrapin bycatch. turtle was marked by filing a unique series of notches in the marginal scutes (Cagle 1939); recaptures were noted. The number of fish in each pot was recorded and all live bycatch Materials and Methods was set free. Any dead fish remaining in pots were removed, and no bait remained in pots after the second day. Study Area Terrapin Population Estimate The experiment was conducted over the period beginning 4 June 2009 and ending 31 July 2009, with all sampling In addition to pots placed in the subtidal creeks, we placed ten completed in the upper reaches of Felgates Creek, a commercial pots fitted with 60-cm chimneys in small mesohaline tidal marsh creek connected to the York River, intertidal channels of the vegetated marsh. These pots on the Yorktown Naval Weapons Station (37.2667 remained unbaited throughout the same study period as the N, −76.5850 W). The surrounding wetland complex is BRD experiment and were sampled approximately 6 days dominated by the marsh grass Spartina alterniflora. each week of the study. All newly captured terrapins were Commercial and recreational crabbings have not been sexed and measured for carapace width and shell depth, allowed in Felgates Creek for over 40 years (Rook et al. marked with a unique code using the notching technique, and 2010). then released at the point of capture. Recaptures were noted, and population size was estimated using the Schnabel mark– Bycatch Experiment recapture method (Krebs 1989). We placed ten pairs of commercial crab pots (galvanized steel; Data Analysis commercial and recreational pots require cull rings but these were not used in this study) in the subtidal portions of Felgates All capture data were tested for normality using Shapiro– Creek, to an approximate depth of 60 cm at mean low water so Wilk tests and found to be nonnormally distributed. that the pots were submerged at all times. This shallow Because no transformation led to normalization of the data, subtidal zone is where many recreational crab pots are placed nonparametric tests comparing crab catch and crab sizes in and where some derelict and abandoned pots get carried by BRD versus non-BRD pots were completed using Mann– wave and current action. To ensure that terrapins did not Whitney U tests. Bycatch differences as a function of bait drown when captured, all pots were fitted with sealed poultry day were tested using Kruskal–Wallis analysis of variance. wire “chimneys” that extended 120 cm above the top of the For all tests, the significance criterion was p<0.05. pot. During high tide, captured terrapins swam up the chimney to the water surface to breathe. For each pair of commercial pots, one pot was fitted with Results 12×4.5 cm BRDs (TopME© Products) attached near the interior end of the funnel of all four gapes; the other pot was Bycatch Experiment not fitted with BRDs. Our sampling strategy was designed to test the effect of BRDs and the impact of infrequent pot Throughout the 46 pot sampling days, we caught 1,634 baiting on crab catch and bycatch. Although sampling of pots total crabs, of which 679 were of legal size; male crabs was completed 6 days/week, we baited the pots with fresh comprised 93% of the total catch and 96% of the legal-size 388 Estuaries and Coasts (2011) 34:386–390 catch (Table 1). We caught a mean of 1.78±1.79 SD crabs Likewise, more legal-size crabs were caught on average in per pot per day, with a minimum of zero crabs and a pots without terrapin bycatch (1.49±1.46 versus 0.86±0.90 maximum of 11 crabs. Catch per unit effort (CPUE) for crabs), but the difference was not significant (Mann–Whitney total and legal-size crabs was highest on the first sampling U=170, p=0.306). date following pot baiting (Fig. 1). Over 25% of total crabs were caught on the first day after baiting (Table 1). For Terrapin Population Estimate these seven sampling days immediately after pot baiting, neither the difference in average ± SD CPUE (2.86±2.02 From the unbaited commercial pots placed and sampled in versus 3.33±2.26 crabs) nor legal-size CPUE (1.19±1.35 the intertidal channels of small marsh creeks, we caught versus 1.43±1.40) was significant between BRD and non- 143 terrapins, of which 98 were original captures and 45 BRD pots, respectively (Mann–Whitney U=2,213.5, p= were recaptures.
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